You can inject it into the jaw muscle, but that is usually to treat TMJ. I would inquire with a BOTOX specialist regarding your particular situation.
Inject Botox into the Jaw Muscle or Salivary Glands for Gustatory Sweating?
Doctor Answers 3
Botox for Frey's syndrome or sweating instead of salivating
This is commonly caused when the nerves that produce saliva production are diverted to the skin and produce sweating instead. Injecting the effected skin with Botox will minimize the effect of the nerves on the sweat glands.